The number 18381
18381 is a palindrome: it reads 18381 backwards too. Its prime factorisation is 3 × 11 × 557. Divisors (8): 1, 3, 11, 33, 557, 1671, 6127, 18381.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 18381: a palindrome: it reads 18381 backwards too; a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
18381 is composite. Its prime factorisation is
- 3
The divisors add up to 26784; without 18381 itself that is 8403, so 18381 is deficient (8403 is less than 18381). Euler's totient φ(18381) = 11120 numbers up to 18381 share no factor with it.
- 4
The digits of 18381 add up to 21, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 61 steps to reach 1.
LaTeX source of the formulas on this page
\[ 18381 = 3 \times 11 \times 557 \]
18381 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 26784 |
| Euler totient φ(n) | 11120 |
| Square | 337861161 |
| Cube | 6210226000341 |
| Square root | 135.576547 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 61 |
| Scientific notation | 1.8381 × |
18381 in other forms
| Form | Value |
|---|---|
| In words | eighteen thousand three hundred and eighty-one |
| Binary (base 2) | 100011111001101 |
| Octal (base 8) | 43715 |
| Hexadecimal (base 16) | 47CD |
| Base 3 | 221012210 |
| As time | 18381 seconds = 5 h 6 min 21 s |
Is 18381 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | No (remainder 1) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (18381 ÷ 3 = 6127) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 1) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 1) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 6) | A number is divisible by 7 if double the last digit and subtract it from the rest: the result is a multiple of 7. |
| 8 | No (remainder 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 3) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | Yes (18381 ÷ 11 = 1671) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 18381 a prime number?
No. 18381 = 3 × 11 × 557, so it is divisible by 3.
What are the factors of 18381?
1, 3, 11, 33, 557, 1671, 6127, 18381.
What is 18381 in binary?
100011111001101 (hexadecimal 47CD, octal 43715).
What is the square root of 18381?
About 135.5765.
Is 18381 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 18381?
18381 is a palindrome: it reads 18381 backwards too; a happy number: repeatedly adding the squares of its digits reaches 1.